This is a cable tensioning mechanism and more specifically is a mechanism which tensions the cable of a typewriter during use and automatically resets the tensioner when the power is turned on.
The function of a cable snubber mechanism is to control momentary cable slack caused by carriage acceleration and deceleration forces acting on the cable. Cable slack, if allowed to occur, reduces the maximum speed at which the carriage can be incrementally positioned and also reduces the positional accuracy of each incremental carriage position.
Various automatic tensioning devices are in common use for tensioning driving means such as cables, chains, belts, etc. The most common case is that wear and age stretch the driving means, and an automatic snubbing mechanism is required to maintain the slack in the system to a predetermined optimum level.
There is, however, a class of mechanisms in which this automatic tensioning system is not the optimum solution. That is where the length of the driving means is a function not only of age and wear but also of the temperature of the cable. An example of this is in a typewriter, where the internal temperature slowly increases during the day, and drops overnight when the typewriter is not in use. Since the length of the cable is affected by the internal temperature of the typewriter, if the cable is properly tensioned at the end of the day, it will be overly tensioned when the typewriter is first turned on in the morning. A major parameter determining the operational life of cable wrapped around small pulleys is cable tension. Operating the cable at too great a tension exceeds the cable tensile strength limits, reducing its useful life. What is required is a cost effective method of controlling the cable tensioning mechanism to compensate for temperature.